Conventional phthalocyanine compounds exhibit excellent photoconductivity and are used in electrophotographic photoreceptors, for example. Laser printers which use laser light in place of white light as a light source and have such advantages as high speed, high picture quality and no impact have been widely used in recent years and the development of a photoreceptor for use in such laser printers is now undertaken energetically. Most of them employ a system which uses a semiconductor laser whose progress has been remarkable in recent years as a light source and a photoreceptor which has high sensitivity to light having a long wavelength of 780 nm or so, the wavelength of the light source, is strongly desired. Under the circumstances, there have been reported some phthalocyanine compounds (1) which can be relatively easily synthesized, (2) which have an absorption peak of a long wavelength of 600 nm or more, and (3) which change in spectral sensitivity according to their center metal and crystal form and exhibit high sensitivity at the wavelength range of a semiconductor laser. Thus, the research and development of phthalocyanine compounds are under way energetically.
Phthalocyanine compounds differ from one another in absorption spectrum and photoconductivity according not only to type of their center metal but also to their crystal form. It is known that, when phthalocyanines having the same center metal differ in crystal form, their photoconductivities are greatly affected. For example, in the case of copper phthalocyanine, crystal forms such as .alpha., .gamma., .epsilon., .pi., .chi., .tau., .rho. and .delta. other than a .beta. stable form are known and it is known that these crystal forms can be shifted according to mechanical distortion, sulfuric acid treatment, organic solvent treatment, heat treatment and the like (see "Phthalocyanine" of organic Electronics Materials Series 6). Japanese Laid-open Patent Application No. Sho 50-38543 discloses the crystal forms and electrophotographic properties of copper phthalocyanine and teaches that an .epsilon. form shows the highest sensitivity when .alpha., .beta., .gamma., and .epsilon. forms are compared.
As for hydroxymetal phthalocyanines, U.S. Pat. No. 4,557,989 discloses electrophotographic photoreceptors which comprise dihydroxygermanium phthalocyanine, dihydroxytin phthalocyanine and dihydroxysilicon phthalocyanine. Japanese Laid-open Patent Application No. Hei 6-214415 also reports electrophotographic photoreceptors comprising hydroxy metal phthalocyanines (Al, Ga, In, Si, Ge, Sn) and suggests one crystal form for dihydroxysilicon phthalocyanine.
However, even the dihydroxysilicon phthalocyanine having the above crystal form has problems in dispersibility, applicability of its dispersion and storage properties and cannot achieve sufficient electrophotographic properties such as charge acceptance. Even a phthalocyanine compound which has been proposed in the prior art is not satisfactory in terms of photosensitivity and durability when it is used as a photoconductive material. Therefore, the development of a phthalocyanine compound having a new crystal form is strongly desired. The present invention has been made in view of the above circumstances and it is an object of the present invention to provide a phthalocyanine compound having a new crystal form, which is excellent in photosensitivity, durability and environmental capability as a photoconductive material and an electrophotographic photoreceptor having high sensitivity, durability and stability.
A dihydroxy silicon phthalocyanine compound is produced in accordance with an acid paste or acid slurry method in which a corresponding halogenated silicon phthalocyanine compound is dissolved in sulfuric acid or a slurry of the compound is prepared and the solution or slurry is injected into a poor solvent such as water, or a method in which the compound is treated with an alkali such as sodium hydroxide, potassium hydroxide or ammonia water. In these methods, as large quantities of an acid, alkali and by-produced salt are present in the system, an operation for removing these is required. In many cases, a large quantity of water is used to wash the compound several times, thereby causing many problems in operation, exhaust water disposal and productivity. A salt or the like contained in phthalocyanine crystals cannot be removed with ease, thereby causing problems in the dispersibility of a pigment and the storage and applicability of its dispersion and making it impossible to achieve sufficient electrophotographic properties such as charge acceptance, sensitivity and low residual potential.